Low-Gloss Dry-Erase Coating Formulation

ABSTRACT

An EB (electron beam) or UV (ultra violet) curable, low-gloss, dry-erase coating formulation for static and electronic whiteboards is disclosed. The coating contains an acrylate silica blend, an aliphatic urethane acrylate or a polyester acrylate, a polyfunctional reactive diluent and at least one photoinitiator

RELATED APPLICATIONS

This is a divisional application of Ser. No. 11/767,139, filed Jun. 22,2007 for “Low-Gloss Dry-Erase Coating Formulation,” and now U.S. Pat.No. ______.

BACKGROUND

The present invention relates to a low-gloss dry-erase coatingformulation. More specifically, the invention relates to an EB (electronbeam) curable or UV (ultra violet) curable, low-gloss, dry-erase coatingformulation. The invention further relates to methods of manufacturingthe low-gloss dry-erase coating formulation.

Dry-erase boards also referred to as “whiteboards”, have become popularreplacements to paper and chalkboards, as they are convenient,inexpensive, and versatile. Additionally, whiteboard surfaces can becombined with optical and electronic capabilities to produce surfacesfrom which the images can be reproduced, either on paper or digitally.Because of the capabilities that go far beyond those of traditionalwhiteboards, electronic whiteboards are also gaining popularity.

EB/UV-curable coatings are desirable for dry-erase surfaces as they areabrasion resistant and smooth. These EB/UV-curable coatings, however,produce high gloss surfaces. High gloss surfaces tend to createeyestrain and are difficult to see from certain angles. Thus, in manyapplications, low-gloss surfaces are desirable as they reduce eyestrainand can be viewed more easily from different angles.

The gloss in the coatings can be reduced by roughening the coatingthrough the process of embossing or wrinkling. Gloss can also be reducedby introducing additives (i.e., matting agents such as silica). Surfaceroughening, however, may introduce sites that trap stains and inks andproduce “ghosting”, i.e., a residual image of previously writtenmaterial that remains after the writing is erased.

In addition, the gloss-reducing additives when added to the coatingformulation tend to disperse imperfectly. Thus, dispersing equipment anddispersing agents, such as surface tension modifiers, are required forevenly dispersing these additives in the coating formulation.

In view of the aforementioned, it is desirable to minimize the use ofboth i.e., the surface roughening agents and the dispersing equipmentand/or dispersing agents in the coating formulation.

It is further desirable to have an EB/UV curable, low-gloss, dry-erasecoating formulation that are used to form hardcoats with minimal orpreferably no “ghosting”.

Several patents disclose dry-erase compositions:

U.S. Pat. No. 6,476,965 (He et al.) discloses a dry erasable substrateand projection screen having a dry-erase low-gloss top layer, apigmented layer, and a bead matrix layer comprising glass beads. The dryerasable top layer as disclosed in this invention, however, containsadditives such as flatting agents that require dispersing agent andequipment to evenly disperse these additives. Further, it includes apigmented layer and a bead matrix layer to form the low-gloss,dry-erasable article.

U.S. Patent Application No. 2004/0077497 (Korane et al.) disclosesdry-erase surfaces produced from heat-cured resins. The dry-erasesurfaces in this invention, however, use additives (e.g. flatting agentslike amorphous precipitated silica) to reduce gloss. Thus, thecomposition disclosed in this application requires dispersing agents toevenly disperse the additives. Further, the reduced gloss, dry-erasesurface as disclosed in this application is produced from heat-curedresins.

There is a need for an EB/UV-curable dry-erase coating formulation thathas very low-gloss and yet minimizes the use of surface rougheningagents, additives, dispersing equipment and/or dispersing agents.

There is a further need for EB/UV-curable low-gloss, dry-erase coatingformulation that has enhanced dry-erase properties yet has superiorwritability (i.e., a marker is able to wet the dry-erase surface formedfrom the present coating formulation without dewetting or reticulation.)

There is a further need for EB/UV-curable low-gloss, dry-erase coatingformulation that is capable of forming into a hard, abrasion andchemical resistant coating and yet is substantially flexible.

SUMMARY

In one aspect, the present invention is an EB/UV-curable, low-gloss,dry-erase coating formulation for static dry-erase boards.

In another aspect, the present invention is dry-erase coatingformulation for dynamic surfaces (e.g., electronic whiteboards).

In another aspect, the present invention is an EB/UV-curable low-gloss;dry-erase hardcoat formed from the coating formulation of the presentinvention that has enhanced dry-erase properties yet has superiorwritability.

In yet another aspect, the present invention is an EB/UV-curablelow-gloss, dry-erase coating formulation that is capable of forming intoa hard, abrasion and chemical resistant hardcoat and yet issubstantially flexible.

In yet another aspect, the present invention is a static dry-erase boardprepared with the aforementioned coating formulation.

In yet another aspect, the present invention is an electronic whiteboardprepared with the aforementioned coating formulation.

The foregoing, as well as other objectives and advantages of the presentinvention and the manner in which the same are accomplished, are furtherspecified within the following detailed description and its accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting gloss values versus the concentration ofPHOTOMER® 5010 (i.e., a blend of polyester acrylate, an aliphaticacrylate, acrylic monomer, and silica) for the hardcoat formed from thecoating formulation of the present invention.

FIG. 2 is a graph depicting the gloss values versus coating weight forthe coating formulation of the present invention.

DETAILED DESCRIPTION

The present invention is an EB/UV-curable low-gloss coating formulationfor coating dry-erase whiteboards (e.g., static and electronicwhiteboards).

In one embodiment, the invention is a coating formulation formed from anacrylate silica blend (i.e., a blend of a polyester acrylate, analiphatic acrylate, acrylic monomer, and silica), a urethane acrylate ora polyester acrylate, and a polyfunctional reactive diluent.

The coating formulation according to the present invention may furtherinclude at least one photoinitiator for UV-curable applications.

In addition, the coating formulation may include a polymeric dispersantfor evenly dispersing various ingredients (e.g., silica) of the coatingformulation.

The acrylate silica blend (e.g., PHOTOMER® 5010) in the coatingformulation is the primary gloss reducing binder in the EB/UV-curabledry-erase coating formulation. It produces low-gloss EB/UV-curablehardcoats in difficult to matte EB/UV coatings while eliminating theneed for dispersing equipment and handling silica. This formulatedproduct can be incorporated into the coating formulation by simplemixing. In addition, this formulated product forms an incompatible phaseduring curing to produce microroughness. The presence of silica as wellas the microroughness formed from the incompatible phase may beresponsible for the low gloss values of the present coating formulation.

The aforementioned acrylate silica blend typically includes dipropyleneglycol diacrylate in an amount between about 30 to 50 weight percent ofthe blend. Further, it may include isodecyl acrylate in an amountbetween about 10 to 30 weight percent of this blend. In addition, apolyester acrylate may be added to the silica blend in an amount betweenabout 30 to 50 weight percent of the blend. The aliphatic acrylate istypically responsible for forming an incompatible phase during curing toproduce microroughness. The coating may further contain silica in anamount between about 0.1 to 20 weight percent of the blend. The silicaalso contributes to the microroughness that occurs as the hardcoat isformed.

Typically, for the hardcoat formed from this coating formulation, glossis inversely proportional to the concentration of the acrylate silicablend. See FIG. 1, which plots 60-degree gloss versus concentration ofPHOTOMER® 5010 as applied at 4.9-5.0 lbs/ream (wherein one ream is equalto 3000 sq.ft.).

In one embodiment, the acrylate silica blend is present in the coatingformulation in an amount between about 25 and 65 percent by weight.Typically, the acrylate silica blend is present in the coatingformulation in an amount between about 30 and 50 percent by weight(e.g., between about 35 and 45 percent by weight).

An aliphatic urethane acrylate (e.g., PHOTOMER® 6019, PHOTOMER® 6010,PHOTOMER® 6210, and PHOTOMER® 6184) may be added to the acrylate silicablend to improve the properties of cured coatings produced from thecoating formulation of the present invention. For instance, an aliphaticurethane acrylate may be added to enhance the non-yellowingcharacteristics of the coating film (i.e., the hardcoat) formed from thecoating formulation of the present invention. Those skilled in the artwill recognize the benefits of using aliphatic versus aromatic urethaneacrylates for their non-yellowing characteristics. Further, aliphaticurethane acrylates may enhance physical properties of the coatingformulation such as scratch, scuff, and mar resistance.

In another embodiment, a polyester acrylate (e.g., PHOTOMER® 5429) maybe added to the coating formulation instead of an aliphatic urethaneacrylate.

The aliphatic urethane acrylate (alternatively, a polyester acrylate)may be present in the coating formulation in an amount between about 5and 35 percent by weight. Typically, the aliphatic urethane acrylate ispresent in the coating formulation in an amount between about 10 and 30percent by weight. More typically, the aliphatic urethane acrylate ispresent in the coating formulation in an amount between about 15 and 25percent by weight.

A polyfunctional reactive diluent (e.g., PHOTOMER® 4399) may be added tothe coating formulation of this invention to further enhance theproperties of cured coatings/hardcoats. This may be added for improvingabrasion and scratch resistance of the cured coatings. These compoundsmay also impart hardness to the cured coatings.

Those skilled in the ordinary art would recognize that a polyfunctionalreactive diluent such as a pentafunctional acrylate monomer wouldincrease crosslink density and therefore the hardness, toughness, andchemical resistance, in general when reacted with other oligomers andmonomers. In this regard, those skilled in the art would know thatoligomers, as defined by the International Union Of Pure and AppliedChemistry, are “molecule(s) of intermediate relative molecular mass, thestructure of which essentially comprises a small plurality of unitsderived, actually or conceptually, from molecules of lower relativemass.” (1996 IUPAC, PURE AND APPLIED CHEMISTRY 68, 2287-2311) Thus, thepolyfunctional reactive diluent may be added to the coating formulationto increase the crosslink density of the coating during polymerization,using either EB or UV radiation, by linking together the oligomerspresent in the formulation.

Further, the polyfunctional reactive diluent may also impart enhanceddry-erase properties to the present coating formulation.

In one embodiment, the polyfunctional reactive diluent is present in thecoating formulation in an amount between about 20 and 50 percent byweight. Typically, the polyfunctional reactive diluent is present in thecoating formulation in an amount between about 25 and 45 percent byweight. More typically, the polyfunctional reactive diluent is presentin the coating formulation in an amount between about 30 and 40 percentby weight.

Photoinitiators may be included in the coating formulation to initiatephotopolymerization of chemically unsaturated prepolymers (e.g., thepolyester acrylate oligomers) in combination with monofunctional ormultifunctional monomers. When exposed to UV radiation, photoinitiatorsabsorb light to produce free radicals. These free radicals initiate thepolymerization of the unsaturated compounds in the coating formulation.Examples of non-yellowing and minimal yellowing photoinitiators that maybe used in the coating formulation of the present invention include butare not limited to α-hydroxyketones such as Ciba® DAROCUR® 1173 andCiba® IRGACURE® 184.

Photoinitiators may be present in the coating formulation in an amountbetween about 0.5 and 5 percent by weight. Typically, thephotoinitiators are present in the coating formulation in an amountbetween about 1.5 and 4.5 percent by weight.

Generally, more than one photoinitiator[s] may be added to UV-curablecoating formulation of the present invention. Typically, at least twophotoinitiators may be added to the coating formulation.

In addition, a polymeric dispersant such as a carboxyl functionalpolymer may be added to stabilize the silica in the coating formulationto prevent agglomeration that may cause coating streaks duringapplication of the coating formulation. More typically, a carboxylfunctional polyacrylate (e.g., TEXAPHOR® 3250) may be used as apolymeric dispersant due to its compatibility with the other compoundsof the coating formulation.

The polymeric dispersant may include a solvent e.g., heavy aromaticnaphtha (CAS 64742-94-5). It may further include propylene glycol methylether acetate.

This polymeric dispersant may be present in the coating formulation inan amount between about 0.01 and 1.5 percent by weight. Typically, thepolymeric dispersant may be present in the coating formulation betweenabout 0.05 to 1 percent by weight.

Depending upon the technique used for coating a surface, the presentformulation may be dissolved in a solvent (i.e., t-butyl acetate,ethanol, toluene, ethyl acetate, isopropyl alcohol, toluene and theirblends).

Typically, exempt solvents such as t-butyl acetate are preferred forinclusion in the present coating formulation. Those skilled in theordinary art would appreciate that these types of solvents are preferredas they are exempt from regulation by the EPA as VOC's (Volatile OrganicCompounds) since they have been determined scientifically not tocontribute to the formation of ozone and thus are environment friendly.Of course, non-exempt solvents may also be used if compatible with theingredients of the present coating formulation.

In another embodiment, the present invention is a low-gloss dry-erasehardcoat that includes at least a portion of a substrate coated with theaforementioned coating formulation.

The substrate of the dry-erase hardcoat is typically formed of polymericmaterial (e.g., polyethylene terephthalate, polycarbonate, melamine,porcelain, coated paper, metal, and glass).

For example, DuPont Melinex 339 PET, White, 500 gauge, may be used as asubstrate.

Generally, a substrate that is pre-treated on at least one side is usedin the hardcoat formed from the present invention. This type ofpre-treated polyester has enhanced adhesive properties. For instance,pre-treated polyesters such as white polyester and clear polyester maybe used as substrates. Additionally films may be treated to improvehardcoat adhesion using corona discharge (i.e., an electrical dischargeaccompanied by ionization of atmospheric oxygen, which oxidizes thesurface of the substrate, increases substrate surface tension, andimproves its adhesive properties) or something similar.

In one aspect, the hardcoat formed from the coating formulation of thepresent invention may include a low-gloss of less than about 40 glossunits measured at 60 degrees. In some coating formulations, the glossmay be less than about 30 gloss units measured at 60 degrees.

Those skilled in the art know that specular gloss, i.e., the mirror-likereflection of light from a surface, is typically measured at anincidence angle of 60, 85, or 20 degrees using gloss meters. Forinstance, a 60-degree Novogloss gloss meter was used to measure thegloss of the coating formulation and the hardcoat of the presentinvention. The Novogloss unit is distributed by Paul N. Gardner Companyin Pompano Beach Fla. It is manufactured by a UK company called RhopointInstrumentation. With respect to measurement, an internal test methodbased on ASTM D2457 was used.

Those of ordinary skill in the art would appreciate that one of thevariables affecting gloss is coating weight. Surprisingly, the gloss ofthe aforementioned hardcoat decreases as the coating weight decreases.See FIG. 2, which plots 60-degree gloss versus the amount deposited inpounds per ream (lbs/ream) at a concentration of PHOTOMER® 5010 of 52.2%by weight. For the hardcoat formed from the aforementioned coatingformulation, gloss is proportional to coating weight. Typically, atconcentrations of the acrylate silica blend in the amount of betweenabout 30 and 65 percent by weight of the coating formulation, the target60 degrees gloss of between about 15 and 35 is obtained at coatingweight of between about 1 and 10 lbs/ream.

FIG. 2 illustrates that when the hardcoat formed from the coatingformulation of the present invention has a coating weight of betweenabout 1 and 10 lbs/ream, the hardcoat has a gloss value of less thanabout 40 gloss units measured at 60 degrees. More preferably, at coatingweight of between about 4 and 6 lbs/ream, the gloss value is less thanabout 35 gloss units measured at 60 degrees.

In another embodiment, the present invention is a dry-erase whiteboardthat includes the aforementioned coating formulation, a substrate, and abacking board. Typically, the backing boards used in these whiteboardsmay be formed of polymeric material, such as polyethylene terephthalate,polycarbonate, melamine, porcelain, coated paper, metal, wood, or glass.

The hardcoat formed from the coating formulation of the presentinvention has enhanced dry-erase properties yet it demonstrates superiorwritability (i.e., a marker is able to wet the dry-erase surface formedfrom the present coating formulation without dewetting or reticulation.)

Table 1 (below) demonstrates some key optical and physical properties ofthe present dry-erase coating formulation:

TABLE 1 60 DEGREE 60 DEGREE GLOSS, GLOSS, PENCIL FLEXI- CROSS- MACHINETRANSVERSE HARD- BILITY, HATCH DIRECTION DIRECTION NESS ½″ BAR ADHESION30.6 29.5 HB NO 5b, PASS CRACKING

To assess writing quality and completeness of erasure, dry-erase markersfrom different manufacturers were evaluated (e.g., Expo 2 Dry-erasemarker of Sanford Corporation, Oak Brook, Ill. 60523; and AveryMarks-A-Lot Whiteboard Dry-erase marker of Avery Dennison Corporation;Brea, Calif. 92821).

Red, blue, green, and black color markers were evaluated. A dry-erasesurface coated with a composition according to the present invention wasmarked with each of the above-referenced color test marker and allowedto dry for at least one minute and then erased using erasers from therespective named manufacturers.

The results indicated that all markers tested displayed good writability(e.g., wetting of the dry-erase surface).

The results further indicated that the ink on the dry-erase surface waseasily removable and that the erasers from the same manufacturersdemonstrated good erasibility.

In a second experiment, the chemical resistance of the dry erase surfaceformed from the coating formulation of the present invention wasevaluated by rubbing the dry erase surface with a Methyl-Ethyl-Ketone(i.e., MEK) saturated Webril Wipe (Fiberweb plc Corporate Office—London,1 Victoria Villas Richmond GW2 9TW) a minimum of 30 cycles. Afterallowing the surface to dry, the writing and dry erase properties wereevaluated using the above-named colors of test markers and erasingdevices. In all cases, each marker displayed good writability anderasibility using the test devices.

In addition, the 60-degree gloss value after rubbing the dry-erasesurface with MEK saturated Webril Wipe was also evaluated to determineif surface gloss had been impacted. The 60-degree gloss values remainedin the range of less than 35 gloss units.

The data in Table 1 further indicates that the dry-erase coating appliedto polyester film formed from the coating formulation according to thepresent invention did not crack during processing using a half-inch bar(i.e., A flexibility test was performed by cycling a 1″×12″ test stripof the dry-erase coating, applied to a polyester film substrate formedfrom the formulation of the present invention, such that the non-coatedside of the substrate was wrapped around ˜50% of the ½″ bar, and cycledback and forth much like a belt on a pulley. After 10 cycles the coatingwas not damaged (no visual cracking, flaking, or loss of adhesion).Those skilled in the art will understand that coatings that withstandthis test without cracking, flaking, or losing of adhesion aresubstantially flexible.

In yet another aspect, the invention is a process for providinglow-gloss dry-erase hardcoat from the aforementioned coatingformulation. Several coating methods suitable for coating flexiblesubstrates in a roll-to-roll process including roll coating, gravurecoating, meyer rod coating, and slot die coating can be used.

Typically, the slot die method is used due to its precision of coatingweight control. This includes applying the coating formulation to apre-treated substrate (e.g., web with good adhesion). The substratealong with the coating formulation is then dried in an oven. Thisvaporizes the solvent in the formulation. Thereafter, the coating iscured by exposing it to EB/UV radiation.

In one aspect, the coating may also be cured by exposing it to EB/UVradiation. This may be done under a nitrogen atmosphere. Those ofordinary skill in the art would know that excluding oxygen with nitrogeninerting helps prevent undesirable reactions with oxygen that leads toan under cured coating, which impacts hardness and enhanced dry eraseproperties.

In the specification and drawings, typical embodiments of the inventionhave been disclosed and, although specific terms have been employed,they have been used in a generic and descriptive sense only and not forpurposes of limitation.

1. A low-gloss dry-erase coating formulation comprising a mixture of: anacrylate silica blend for reducing gloss by blending silica and byforming an incompatible phase during curing to produce microroughness;an acrylate selected from a group consisting of an aliphatic urethaneacrylate and a polyester acrylate for enhancing physical properties ofthe mixture; and a polyfunctional reactive diluent for increasingcrosslink density and the hardness, toughness, and chemical resistanceof the surface coated with said mixture, when reacted with otheroligomers and monomers of said mixture.
 2. A coating formulationaccording to claim 1, further comprising at least one minimal-yellowingphotoinitiator for initiating photopolymerization of chemicallyunsaturated prepolymers and monomers of said mixture.
 3. A coatingformulation according to claim 2, comprising at least twophotoinitiators.
 4. A coating formulation according to claim 3, whereinsaid photoinitiator comprises 2-hydroxy-2-methyl-1-phenyl-propan-1-one.5. A coating formulation according to claim 3, wherein saidphotoinitiator comprises 1-hydroxy-cyclohexyl-phenyl-ketone.
 6. Acoating formulation according to claim 2, wherein said photoinitiatorcomprises α-hydroxyketone.
 7. A coating formulation according to claim2, wherein said photoinitiator is present in an amount between about 0.5and 5 percent by weight.
 8. A coating formulation according to claim 2,wherein said photoinitiator is responsive to ultraviolet radiation.
 9. Acoating formulation according to claim 1, further comprising a polymericdispersant for stabilizing the silica in said mixture.
 10. A coatingformulation according to claim 9, wherein said polymeric dispersantcomprises a carboxy functional polyacrylate.
 11. A coating formulationaccording to claim 9, wherein said polymeric dispersant is present in anamount between about 0.05 and 2 percent by weight.
 12. A coatingformulation according to claim 1, further comprising a solventcompatible with said mixture.
 13. A coating formulation according toclaim 12, wherein said solvent is selected from the group consisting ofacetates, aromatics, and their combinations thereof.
 14. A coatingformulation according to claim 1, wherein the acrylate silica blendcomprises: dipropylene glycol diacrylate in the amount of between about30 and 50 weight percent of said blend; isodecyl acrylate in the amountof between about 10 and 30 weight percent of said blend; a polyesteracrylate in the amount of between about 30 and 50 weight percent of theblend; and silica in the amount of between about 0.1 to 20 weightpercent of the blend.
 15. A coating formulation according to claim 1,wherein the acrylate silica blend is present in said coating formulationin an amount between about 25 and 65 percent by weight.
 16. A coatingformulation according to claim 1, wherein the acrylate silica blend ispresent in said coating formulation in an amount between about 30 and 50percent by weight.
 17. A coating formulation according to claim 1,wherein said aliphatic urethane acrylate comprises: urethane acrylate inthe amount of between about 40 to 60 weight percent of said aliphaticurethane acrylate; and tripropyleneglycol diacrylate in the amount ofbetween about 40 to 60 weight percent of said aliphatic urethaneacrylate.
 18. A coating formulation according to claim 1, wherein saidaliphatic urethane acrylate is present in said coating formulation in anamount between about 5 and 35 percent by weight.
 19. A coatingformulation according to claim 1, wherein said polyester acrylate ispresent in said coating formulation in an amount between about 5 and 35percent by weight.
 20. A coating formulation according to claim 1,wherein said polyfunctional reactive diluent comprises polyfunctionalerythritol polyacrylates.
 21. A coating formulation according to claim1, wherein said polyfunctional reactive diluent comprisesdipentaerythritol monohydroxy pentaacrylate.
 22. A coating formulationaccording to claim 1, wherein said polyfunctional reactive diluent ispresent in said coating formulation in an amount between about 20 and 50percent by weight.
 23. A coating formulation according to claim 1,wherein said polyfunctional reactive diluent is present in said coatingformulation in an amount between about 30 and 40 percent by weight. 24.An electron beam curable coating formulation according to claim
 1. 25. Alow-gloss dry-erase coating formulation comprising: an acrylate silicablend present in the coating formulation in an amount between about 25and 50 percent by weight; an acrylate selected from a group consistingof an aliphatic urethane acrylate and a polyester acrylate present inthe coating formulation in an amount between about 5 and 30 percent byweight; a polyfunctional reactive diluent present in the coatingformulation in an amount between about 25 and 45 percent by weight; andat least one photoinitiator present in the coating formulation in anamount between about 0.5 and 4.5 percent by weight.
 26. A low-glossdry-erase coating formulation according to claim 25, further comprisinga polymeric dispersant present in the coating formulation in an amountbetween about 0.05 and 1.5 percent by weight.
 27. A low-gloss dry-erasecoating formulation according to claim 25, further comprising a solvent.28. A process for making a low-gloss dry-erase hardcoat comprising:applying a low-gloss coating formulation that includes an acrylatesilica blend, an acrylate selected from a group consisting of analiphatic urethane acrylate and a polyester acrylate, a polyfunctionalreactive diluent, at least one photoinitiator, a polymeric dispersant,and a solvent on a pre-treated substrate; drying said solvent from saidcoating formulation; and exposing said coating formulation on saidpre-treated substrate to a radiation selected from a group consisting ofelectron beam and ultra violet radiation.
 29. A process according toclaim 28, wherein the step of drying the solvent from the coatingformulation comprises drying by heat treatment of the coatingformulation.